Glutaric acidemia type I (GA-I) is an inherited disorder of amino acid metabolism, which in its usual form, causes a progressive extrapyramidal movement disorder and death during the first decade of life. We have recently generated a mouse model of GA-I via gene targeting in embryonic stem cells. The affected mice demonstrate many of the phenotypic features seen in GA-I patients. The goal of this proposal is to use this animal model to answer a fundamental question regarding the pathophysiology of GA-I. Specifically, is the neurologic damage the result of circulating levels of toxic metabolites, or due to the lack of glutaryl CoA-dehydrogenase (GCDH) activity within individual neurons (i.e. is it a cell autonomous phenotype). The specific aim of this proposal is to test the hypothesis that expression of the GCDH cDNA in the liver of Gcdh 1" mice will normalize the circulating levels of toxic metabolites (glutaric and 3-OH glutaric acids), and prevent the development of the myelinopathy and motor deficits seen in these animals. The approach we will use is to express the Gcdh cDNA in the liver of Gcdh / animals using the albumin promoter. Current therapy of GA-I consists primarily of a protein-restricted diet, which is based on the assumption that minimizing the levels of glutaric and 3-OH glutaric acids is beneficial. The experiments in this proposal will directly test that assumption. If our hypothesis is correct, the subsequent development of therapies such as liver directed gene therapy and liver stem cell therapy could then begin. Alternatively, if it is determined that normalization of metabolite levels is insufficient to prevent neuropathology in GA-I, alternative approaches to therapy need to be developed.